1. Field of the Invention
The present invention relates to a liquid crystal display, and more particularly to a liquid crystal display that is adaptive for improving picture quality by eliminating residual DC components within a horizontal electric field type liquid crystal display panel.
2. Discussion of the Related Art
Generally, liquid crystal display devices display a natural-like motion picture using thin film transistors TFT as switching devices. Such liquid crystal display devices can be made small-sized in comparison to cathode ray tubes CRT and have been commercialized as potable televisions, notebook computers and the monitors of personal computers.
The liquid crystal display device displays pictures corresponding to video signals like television signals in a pixel matrix or picture element matrix where pixels are arranged at each crossing area of gate lines and data lines. Each pixel includes a liquid crystal cell that controls the amount of transmitted light in accordance with the voltage level of a data signal. The TFT is installed at the crossing area of the gate line and the data line and switches the data signal, which is to be transmitted to the liquid crystal cell, in response to a scan signal, i.e., gate pulse, from the gate line.
Such liquid crystal display device can be classified into a vertical electric field type liquid crystal display device and a horizontal electric field type liquid crystal display device in accordance with the direction of electric field by which liquid crystal is driven, wherein the vertical electric field type liquid crystal display device has an electric field of vertical direction applied and the horizontal electric field type liquid crystal display device has an electric field of horizontal direction applied and a viewing angle widened.
The horizontal electric field type liquid crystal display device, differently from the vertical electric field type liquid crystal display device, has the liquid crystal within a pixel cell rotate on the basis of the horizontal direction by the horizontal electric field, thus there is an advantage that the viewing angle is wide.
FIG. 1 is a diagram representing a signal line of a horizontal electric field type liquid crystal display device of the related art.
Referring to FIG. 1, a lower substrate 2 provided with a TFT array includes a plurality of common lines CL1 to CLm to apply common voltages Vcom to common electrodes, a plurality of gate lines GL1 to GLm to apply gate voltages to gate electrodes, and a plurality of data lines DL1 to DLn to apply data voltages to pixel electrodes.
The common lines CL1 to CLm are a number m of lines formed parallel to the gate lines GL1 to GLm.
The gate lines GL1 to GLm are a number m of lines formed alternate with and parallel to the common lines CL1 to CLm and apply the gate voltages to the gate electrodes of the TFTs.
The data lines DL1 to DLn are a number n of lines formed perpendicularly to the gate lines GL1 to GLm. The data lines DL1 to DLn apply data signals to pixel electrodes through the drain electrodes of the TFTs. Pixel areas are formed at the intersection area of the common line CL and the gate line GL that cross the data line DL. Thin film transistors are also formed at the crossing area of the data line DL and the gate line GL.
Supply lines SL are formed at both sides of the lower substrate 2 in a perpendicular direction at least to the gate lines GL1 to GLm. The supply lines SL apply common voltages to the common line CL. A static electricity prevention circuit 4 and 8 is installed between the supply line SL and signal lines including the gate line GL, the data line DL and the common line CL.
The gate lines GL1 to GLm and the data lines DL1 to DLn of the horizontal electric field type liquid crystal display device of the related art are frequently broken because of manufacturing tolerance and operational error. When the gate line GL1 to GLm is broken, some of the TFTs are not driven. When the data line DL1 to DLn is broken, the data signal is not applied to some of the TFTs. To determine if there are broken lines in the gate lines GL1 to GLm and the data lines DL1 to DLn, the TFT array substrate is inspected with a test circuit (not illustrated). After completing the test, a residual DC component within the liquid crystal display panel is bypassed through the supply line SL to be eliminated.
On the other hand, whether the TFT runs normal or not is detected with an output voltage value obtained by applying voltage to each of a gate shorting bar 12 and a data shorting bar 10 in order to test the operation of the TFT.
The gate shorting bar 12 is connected to at least any one of the gate lines GL and the common lines CL, and the data shorting bar 10 is connected to the data DL. At least any one of the gate line GL and the common line GL connected to the gate shorting bar 12 is connected to the supply line SL through a static electricity prevention circuit 4 and the data line DL connected to the data shorting bar 10 is connected to the supply line SL through the static electricity prevention circuit 4. The supply line SL surrounds the display area of the lower substrate 2 and is connected to the static electricity prevention circuit 4 and 8 that is formed at both ends of each of the data line DL, the gate line GL and the common line CL.
In this way, the related art liquid crystal display panel has a bypass loop formed through the supply line SL. A DC component and a power off signal remaining within the liquid crystal display panel is bypassed through the bypass loop and naturally discharged.
However, if there is poor a contact between the bypass loop and the signal lines or if there is a defect in the bypass loop, the remaining DC component is applied to the display area of the liquid crystal display panel causing contaminant within the liquid crystal display panel to be excited, thereby deteriorating picture quality in the display area. Specifically, stains appear particularly around a liquid crystal injection hole (not shown), thus the picture quality is deteriorated.